1. Field of the Invention
The present invention relates to a remaining fuel alarm for a vehicular fuel-combustion heater for heating, with combustion heat, a heating medium which heats air flowing through a duct having air outlets openable into a passenger's compartment, through heat exchange between the heating medium and the air.
2. Description of the Related Art
In general, air-conditioning systems for use on electric vehicles cannot use a heating medium in the form of cooling water which would otherwise be heated by cooling internal combustion engines. For this reason, for example, a vehicular air-conditioning system is known, which is disclosed in Japanese laid-open patent publication No. 8-197937.
The disclosed air-conditioning system has a duct for passing air therethrough into a passenger's compartment, wherein the air-conditioning system operates selectively in a refrigerating cycle which involves an air blower for delivering air through the duct into the passenger's compartment, a coolant compressor for compressing and discharging a coolant, a coolant-water heat exchanger for heating hot water through heat exchange between the compressed coolant discharged from the coolant compressor and the hot water, and a coolant evaporator for cooling air with the heat of evaporation of the coolant, and in a hot-water cycle which involves a pump for circulating the hot water heated by the coolant-water heat exchanger and a hot-water heater disposed in the duct for heating air flowing through the duct with the hot water flowing from the coolant-water heat exchanger. The hot-water cycle also involves a fuel-combustion heater, connected in series with the hot-water heater, for heating the hot water with heat generated when a fuel is combusted, in order to obtain a sufficient heating capability, for example, in cold climates.
In this case, the fuel-combustion heater obtains the combustion heat for heating the hot water, by combusting the fuel such as kerosene, white gasoline, and gas oil. Therefore, in order to inform the passenger of the fact that the remaining amount of fuel is not more than a predetermined amount, for example, it is necessary to display a message on a panel and give a warning.
Therefore, in general, a remaining fuel alarm is adopted, which is involved in a fuel system for supplying fuel to an automobile engine. For example, as disclosed in Japanese laid-open patent publication No. 8-96269, such an apparatus comprises a thermistor which is disposed corresponding to a predetermined height of liquid level in a fuel tank. The apparatus is constructed such that when the level of the fuel arrives at the predetermined height of liquid level to cause the change in resistance value of the thermistor, then an alarm lamp is switched on, or it is switched on and off.
When the fuel-combustion heater is not used as in the summer season, the fuel is removed from the fuel tank in order to pre vent the fuel system from deterioration. Therefore, the thermistor is always exposed to air in the fuel tank, and the alarm lamp is always switched on (or switched on and off).
As described above, the following problem is pointed out. That is, the state, in which the alarm lamp is always turned on as in the summer season during which the fuel-combustion heater is not used, seriously obstructs the view of the passenger. It may be also conceived that the fuel is stored in the fuel tank throughout the year in order not to turn on the alarm lamp. However, such a countermeasure causes another problem that the fuel system is markedly deteriorated.